This invention relates to a novel CRT (cathode-ray tube) having internal means for suppressing arcing therein during the operation thereof; and particularly for suppressing flashovers in the glass neck of a CRT having an electron-gun mount assembly housed therein.
A color television picture tube is a CRT which comprises an evacuated envelope including a viewing window that carries a luminescent viewing screen thereon, and a glass neck that houses an electron-gun mount assembly therein. During the operation of the tube, the mount assembly produces one or more electron beams for selectively scanning the viewing screen so as to produce a viewable video image thereon. During the operation of the tube, an excessive amount of stray or uncontrolled electron emission and electrical leakage sometimes develops within and/or around the structure of the mount assembly. This condition may result in flashovers, a form of arcing, which may degrade the performance of the tube and/or may be destructive of the tube and/or associated circuitry. Excessive stray or uncontrolled electron emission, leakage and arcing are a result of a combination of factors involving the electrodes and the closely-spaced glass surfaces of the neck.
Various coatings on the internal surfaces of the neck of the tube have been suggested for suppressing such arcing. U.S. Pat. No. 3,355,617 to J. W. Schwartz et al. discloses an internal, electrically-resistive coating of iron oxide or a mixture of oxides of iron and manganese. U.S. Pat. No. 3,758,802 to T. Kubo et al. discloses an internal, electrically-insulative coating of crystallized glass. U.S. Pat. No. 3,979,632 to E. A. Gunning et al. discloses an internal coating of insulative chromic and/or ferric oxide. U.S. Pat. No. 4,285,990 to K. G. Hernqvist discloses an internal, electrically-conductive coating of chromium metal. While each of these internal neck coatings may have a beneficial effect in some tube designs, the beneficial effect has not been great enough to find much commercial use. Some of these coatings are made by processes that are not practical for commercial manufacturing, or are inferior in suppressing arcing. Because of the fabrication process used, some coatings are too thick, causing spalling of the neck glass during subsequent processing. Also, with some coatings, when the tube is electrically processed by spot knocking, undesirable particles of the coating may be released into the tube and may interfere with its proper performance.